Last night on his talk show Conan O'Brien was transformed into everyone's favorite deformed Fratelli brother, Sloth from "The Goonies."

Apparently the movie is a favorite of Johnny Galecki from "Big Bang Theory" (and everyone who grew up in the '80s), who was thrilled to learn parts of the movie were filmed on the same sound stage as Conan's show.

You see where this is headed?

Galecki pleaded for Conan to re-enact a scene between Sloth and Chunk ... and had one crazy impressive Sloth mask ready to go.

Check out the results above!

And find out what happened to the original cast of the 1985 flick below: